This invention relates to therapeutic modalities for treatment of neoplastic disease. More specifically, this invention involves synthetic peptides that selectively destroy malignant and transformed cells, and a method for treatment of neoplastic disease based thereon.
The p53 protein is a vital regulator of the cell cycle. It blocks the oncogenic effects of a number of oncogene proteins that induce mitosis, in part by blocking transcription of proteins that induce mitosis and by inducing the transcription of proteins that block mitosis, and promote apoptosis. Absence of the p53 protein is associated with cell transformation and malignant disease. Haffner, R & Oren, M. (1995) Curr. Opin. Genet. Dev. 5: 84-90.
The p53 protein molecule consists of 393 amino acids. It includes domains that bind to specific sequences of DNA in a DNA-binding domain that consists of residues 93-313. The crystal structure of this region has been determined by x-ray crystallography. Residues 312-393 are involved in the formation of homotetramers of the p53 protein. Residues 1-93 are involved in regulation of the activity and half life of the p53 protein.
The p53 protein binds to another important regulatory protein, the MDM-2 protein. The MDM-gene that encodes the MDM-2 protein is a known oncogene. The MDM-2 protein forms a complex with the p53 protein, which results in the degradation of the p53 protein by a ubiquination pathway. The p53 protein binds to MDM-2 protein using an amino acid sequence that includes residues 14-22 of the p53 protein, which are invariant. The entire MDM-2 protein binding domain of the p53 protein spans residues 12-26. Haffner, R & Oren, M. (1995) Curr. Opin. Genet. Dev. 5: 84-90.
Considering that the MDM-2 protein is the expression product of a known oncogene, it is not surprising that MDM-2 protein is a very important regulatory protein. Moreover, overexpression or amplification of MDM-2 protein has been found in 40-60% of human malignancies, including 50% of human breast tumors. It has been suggested that formation of a complex between the p53 protein and the MDM-2 protein may result in the inhibition of transcription activity of the p53 protein, and thus the anti-tumor effect of the molecule by blocking of an activation domain of the p53 protein, or of a DNA binding site within it. More generally, these and other experimental observations have been interpreted as suggesting that the anti-tumor effect of the p53 protein might be enhanced by peptides capable of interfering with the binding of the MDM-2 protein to the p53 protein. Indeed, a number of investigators have suggested that the MDM-2/p53 complex might be a target for rational drug design. See, e.g., Christine Wasylyk et al., “p53 Mediated Death of Cells Overexpressing MDM2 by an Inhibitor of MDM2 Interaction with p53”, Oncogene, 18, 1921-34 (1999), and U.S. Pat. No. 5,770,377 to Picksley et al.